Gate drive circuit

ABSTRACT

Example circuitry includes: a transformer circuit having first windings and second windings, where the second windings are magnetically orthogonal to the first windings; first transistors to provide a first voltage to a load, where each of the first transistors is responsive to a first control signal that is based on a first signal through a first winding; second transistors to provide a second voltage to the load, where each of the second transistors is responsive to a second control signal that is based on the first through the first winding, and where the first and second control signals cause the first transistors to operate in a different switching state than the second transistors; and control circuitry responsive to signals received through the second windings to control the first transistors and the second transistors to operate in a same switching state.

TECHNICAL FIELD

This disclosure relates generally to a gate drive circuit.

BACKGROUND

A gate drive circuit may be used to drive semiconductor switches (e.g.,transistors) that drive a load, which may be part of a switchingamplifier. For example, the gate drive circuit may control operation ofsets of transistors to provide power to the load.

SUMMARY

Example circuitry may include: a transformer circuit having firstwindings and second windings, where the second windings are magneticallyorthogonal to the first windings; first transistors to provide a firstvoltage to a load, where each of the first transistors is responsive toa first control signal that is based on a first signal through a firstwinding; second transistors to provide a second voltage to the load,where each of the second transistors is responsive to a second controlsignal that is based on the first signal through the first winding, andwhere the first and second control signals cause the first transistorsto operate in a different switching state than the second transistors;and control circuitry responsive to signals received through the secondwindings to control the first transistors and the second transistors tooperate in a same switching state. The example circuitry may include oneor more of the following features, either alone or in combination.

A control circuit may be between each first winding and each first andsecond transistor, where each circuit may be configured to generateeither the first control signal or the second control signal. Thecontrol circuitry may include circuits, each of which may be between asecondary winding and a corresponding transistor.

The first transistors may include a first transistor connected betweenthe first voltage and the load and a second transistor connected betweenthe load and a reference voltage. The second transistors may include athird transistor connected between the first voltage and the load and afourth transistor connected between the load voltage and the referencevoltage. The first transistor and the fourth transistor may beoperational in a same switching state to apply the first voltage to theload, and the second transistor and the third transistor may beoperational in a same switching state to apply the second voltage to theload, where the second voltage is equal in magnitude and opposite inpolarity to the first voltage. The first transistor and the fourthtransistor may be conductive while the second transistor and the thirdtransistor are not conductive, and the first transistor and the fourthtransistor may not be conductive while the second transistor and thethird transistor are conductive. The first transistor, the secondtransistor, the third transistor, and the fourth transistor may be fieldeffect transistors (FETs), with each FET having a control terminal forreceiving either the first control signal or the second control signal.

The control circuitry may be configured to generate a third controlsignal that is applicable to gates of the first and second transistors.Control of the first transistors and the second transistors to be in asame switching state may occur, at most, within 200 nanoseconds of acommand instructing that the transistors operate in a same switchingstate. Control of the first transistors and the second transistors to bein a same switching state may occur, at most, within 100 nanoseconds ofa command instructing that the transistors operate in a same switchingstate.

The example circuitry may include compensation circuitry to reduce noiseresulting from lack of symmetry in magnetic structures making up thetransformer circuit. The first windings and the second windings may besecondary windings of a transformer circuit having at least one primarywinding. The transformer circuit may include a main primary winding andan orthogonal primary winding, with the main primary winding forinducing signals in the first windings and the orthogonal primarywinding for inducing signals in the second windings. The load may bepart of an audio amplifier. The control circuitry may be configured tooverride the first control signal and the second control signal to causethe first transistors and the second transistors to be in a sameswitching state. The control circuitry may be configured to override thefirst control signal and the second control signal to cause the firsttransistors and the second transistors to be non-conductive.

Example circuitry may include: a transformer circuit having firstwindings and second windings, where the second windings are magneticallyorthogonal to the first windings; and control circuitry (i) responsiveto signals in the first windings, to cause application of a firstvoltage and a second voltage to a load, where the application of thefirst voltage and the second voltage is applied at different times andin opposite polarity, and (ii) responsive to signals in the secondwindings to prevent application of either the first voltage or thesecond voltage to the load. The example circuitry may include one ormore of the following features, either alone or in combination.

The example circuitry may include switches that are controllable basedon the signals in the first windings to enable application of either thefirst voltage or the second voltage to the load. The switches may alsobe controllable to open based on the signals in the second windings,thereby preventing application of either the first voltage or the secondvoltage to the load. The first and second windings may be secondarywindings of the transformer circuit, and the transformer circuit mayhave one or more primary windings to receive control signals forcontrolling the circuitry.

Example circuitry may include: a transformer circuit having firstwindings and second windings, with the second windings beingmagnetically orthogonal to the first windings; means responsive to firstcontrol signals that are based on first signals through first windingsto provide a first voltage to a load; means responsive to second controlsignals that are based on the first signals through the first windingsto provide a second voltage to the load, where the first control signalsand the second controls signal cause output of the first voltage to beopposite in polarity to the second voltage; and means responsive tothird signals received via second windings to override the first signalsto cease output of the first voltage or the second voltage from thecircuitry.

Two or more of the features described in this disclosure/specification,including this summary section, can be combined to form implementationsnot specifically described herein.

The circuitry described herein, or portions thereof, can be controlledby a computer program product that includes instructions that are storedon one or more non-transitory machine-readable storage media, and thatare executable on one or more processing devices. The systems andtechniques described herein, or portions thereof, can be implemented asan apparatus, method, or electronic system that can include one or moreprocessing devices and memory to store executable instructions tocontrol the circuitry described herein.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram including an example gate drive circuit.

FIGS. 2 and 3 are circuit diagrams showing current paths through theexample circuitry of FIG. 1 in different modes of operation.

FIG. 4 is a circuit diagram of a transformer circuit having main andorthogonal windings that may be incorporated into a gate drive circuit.

FIG. 5 is a circuit diagram including an example gate drive circuit thatincludes the transformer circuit of FIG. 4.

FIG. 6 is a circuit diagram of an example compensation circuit.

FIGS. 7A through 7G show structures of an example orthogonal transformerthat may be used in the circuitry described herein.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows example of circuitry 100, which includes a gate drivecircuit, switches driven by the gate drive circuit, and an associatedload. Circuitry 100 includes a transformer circuit, in this example,transformer 101 having primary winding 102 and secondary windings 103,104, 105, 106. In this example, four transistors 110, 111, 112, 113 areused to drive a load 116, here an RLC (resistive-capacitive-inductiveload). Transistors 110, 111, 112, 113 are metal oxide field-effecttransistors (MOSFETs); however, any appropriate type of transistor maybe used (e.g., bipolar junction transistors (BJTs) or IGBT's). A singlepulse command into the primary winding of the transformer simultaneouslyprovides outputs to gate drive circuitry for all switching transistors.

Transistor 110 has a drain connected to the high side terminal ofvoltage source V1 120, and a source connected to a first terminal 121 ofoutput circuit 122. Transistor 111 has a drain connected to the highside terminal of voltage source V1 120, and a source connected to asecond terminal 124 of output circuit 122. Transistor 112 has a drainconnected to top terminal 121 of output circuit 122, and a sourceconnected to a reference, in this example, ground 126. Transistor 113has a drain connected to bottom terminal 124 of output circuit 122, anda source connected to a reference, in this example, ground 126.

Transistors 110, 111, 112, 113 also have control terminals, namelyrespective gates 110 a, 111 a, 112 a, 113 a. Applying an appropriatevoltage to a gate drives the corresponding transistor to conduction,thereby allowing current to flow between source and drain. In thisexample, gate 110 a is controlled by applying a signal from secondarywinding 103, gate 111 a is controlled by applying a signal fromsecondary winding 104, gate 112 a is controlled by applying a signalfrom secondary winding 105, and gate 113 a is controlled by applying asignal from secondary winding 106. In one state of operation shown inFIG. 2, transistors 110 and 113 are driven to conduction (withtransistors 111 and 112 non-conducting), thereby creating an electricalpath 201 from voltage V1 120, through transistor 110, through load 116,through transistor 113, to ground 126. In another state of operationshown in FIG. 3, transistors 111 and 112 are driven to conduction (withtransistors 110 and 113 non-conducting), thereby creating an electricalpath 301 from voltage V1 120, through transistor 111, through load 116,through transistor 112, to ground 126. Thus, voltages applied to theload in the different switching states are opposite in polarity.

Transistors 110, 111, 112, 113 are controlled by transformer 101. Inthis example, secondary windings 103, 106 are opposite in orientation tosecondary windings 104, 105. When primary winding 102 is excited with apositive voltage with respect to the dot, secondary windings 103, 106will have a positive voltage (with respect to the dot) induced in them.This will put a positive voltage on gates 110 a, 113 a, causingtransistors 110, 113 to conduct. That same signal results in a negativevoltage being applied to the gates 111 a and 112 a, and, as a result,transistors 111, 112 do not conduct. This results in current flow alongpath 201 of FIG. 2. When primary winding 102 is controlled to have anegative voltage with respect to the dot, secondary windings 104, 105will have a negative voltage (with respect to the dot) induced in them.This will put a positive voltage on to gates 111 a, 112 a, causingtransistors 111, 112 to conduct. That same signal results in a negativevoltage being applied to gates 110 a and 113 a and, as a result,transistors 110, 114 do not conduct. This results in current flow alongpath 301 of FIG. 3.

Circuitry 100, however, does not provide a mechanism for quicklyturning-off (e.g., preventing conduction through) all four transistors110, 111, 112, 113 at the same time or at about the same time. In somecases, a significant amount of additional circuitry may be included toturn-off all transistors at the same time as part of the gate drivecircuit. A downside to this approach is that this amount of additionalcircuitry increases overall circuit complexity and system cost. Bycontrast, the examples described herein, which use orthogonal windings,may be simpler, smaller, less expensive, and require less additionalcircuitry.

Turning-off all four transistors can be beneficial in response to faultconditions, or at normal shutdown to reduce transient noise generation.In this regard, it may be possible to provide no signal through primarywinding 102, which will eventually result in all transistors settlinginto a non-conductive state. However, if transistors are conducting,removal of the signal from the primary winding may not result in thetransistors transitioning to a non-conductive state quickly enough.Instead, there can be a lag, during which time the conductingtransistors remain at least partly conductive. In this regard, it takestime for their gate drive to drop sufficiently to allow the devices toopen. This time is uncontrolled, and possible unwanted states may exist(such as having all transistors conducting). Also, uncontrolled gatedrive voltage might result in an intermediate drive being applied for ashort period of time placing the transistors in a partially conductingstate. This can damage or destroy the devices as large power may bedissipated in the transistors.

A transformer having orthogonal windings may be incorporated into a gatedrive circuit, such as that included in FIG. 1, to turn-off alltransistors controlled by the gate drive circuit at about the same time.The orthogonality of the windings, as described below, can ensure theorthogonal inputs and corresponding outputs do not interfere with eachother. As described below, in example implementations, there aremultiple primary and corresponding secondary windings in thetransformer. One set of primary and corresponding secondary windings (afirst set) is orthogonal to another set of primary and correspondingsecondary windings (a second set). Thus, inputs and correspondingoutputs of the first set to do interfere, or substantially interfere,with inputs and corresponding outputs of the second set

For example, an input to a primary winding of the second set (e.g., aturn off pulse) results in output signals in secondary windings of thesecond set to drive gate turn-off circuitry, but does not produceoutputs in any of the windings of the first set. Similarly, in thisexample, an input to a primary winding of the first set results inoutput signals in secondary windings of the first set, but does notproduce outputs in any of the windings of the second set.

In an example implementation, the transformer having orthogonal windingsmay include two magnetic circuits wound around a single E-core, whichare configured to operate relatively independently. In the examplesdescribed herein, the “orthogonal” part of transformer is configured toproduce one or more signals that are used to operate all transistors ina same switching state, e.g., to enable all of the transistors to beturned-off at about the same time.

In some implementations, the responsiveness to signals produced by theorthogonal windings may be on the order of tens or hundreds ofnanoseconds (ns). For example, in some implementations, the transistorsmay be turned off (e.g., driven to non-conduction) within that period.In some implementations, the transistors all may be turned-off within200 ns, 100 ns, 50 ns, or less following application of a turn offcommand signal to the transformer. In other implementations, thetransistors may be turned-off within a different period of time that isgreater than 200 ns. Thus, the use of orthogonal windings and the gatedrive circuit described herein may result in a reduced turn-off timecompared to the case if a signal is simply removed from the primarywinding of the transformer, which could result in turn-off times in 100s of μs to 100 s of ms.

Referring, to FIG. 4, an example transformer circuit, includingtransformer 400, that may be used in a gate drive circuit is shown. Inthis example, transformer 400 includes primary windings 401. Primarywindings 401 are designated as primary main windings, since signals sentthrough those windings induce signals in corresponding secondary mainwindings to control the operation of a first set of transistors and asecond set of transistors so that the first set of transistors areoperational (e.g., conductive) when the second set of transistors arenon-operational (e.g., non-conductive), and vice versa. In this example,transformer 400 includes secondary windings 404. Secondary windings 404are designated as secondary main windings, since signals in thosewindings are induced by signals the primary main windings to control theoperation of the first set of transistors and the second set oftransistors so that the first set of transistors are operational (e.g.,conductive) when the second set of transistors are non-operational(e.g., non-conductive), and vice versa.

In the example of FIG. 1 above, for example, transistors 110, 113 aredriven to conduction when transistors 111, 112 are non-conductive, andtransistors 111, 112 are driven to conduction when transistors 110, 113are non-conductive. Thus, transistors 110, 111 and 112, 113 are operatedin different switching states from each other by control signalsgenerated via the main windings.

In this example, transformer 400 also includes primary winding 409.Primary winding 409 is designated as a primary orthogonal winding, sinceprimary orthogonal winding 409 defines a magnetic flux path that isorthogonal (or substantially orthogonal) to the magnetic flux path ofprimary main windings 401. Signals sent through primary orthogonalwinding 409 induce signals in corresponding secondary orthogonalwindings to control the operation of transistors controlled by the gatedrive circuit so that all transistors are in a same switching state.Secondary windings 410 are designated as secondary orthogonal windings,since each secondary orthogonal winding 410 is coupled to a magneticflux path that is orthogonal to the magnetic flux path couplingsecondary main windings 404. Signals in secondary orthogonal windings410 are induced by signals in the primary orthogonal winding 409 tocontrol the operation of all transistors to be in a same switchingstate. In this regard, in some implementations, all of the transistorscontrolled by the gate drive circuit are driven to a non-conducing state(a same switching state) by control signals generated via the orthogonalwindings, thereby turning-off the gate drive circuit, and preventing anoutput from the corresponding controlled circuitry. Other types ofswitching state operation may also be commanded using the circuitrydescribed herein or variants thereof.

Examples of the construction of transformers having orthogonal windingsare described in U.S. patent application Ser. No. 13/076,923, filed onMar. 31, 2011, which is incorporated herein by reference.

In the example implementations described herein, there may be little orno magnetic coupling between the main windings and the orthogonalwindings. As such, each set can be operated independently withoutinducing significant voltages in the other set of windings. In someimplementations, signals from the orthogonal windings override signalsfrom the main windings. As described below, even if signals from themain windings instruct different switching state operation of differentsets of transistors, if a signal from the orthogonal windingsinstructing a same switching state operation is generated, the signalfrom the orthogonal windings overrides the signals from the mainwindings, and causes in a same switching state operation of alltransistors in the circuit.

A transformer having orthogonal windings may be incorporated intocircuitry such as that of FIG. 1, and operated in the manner describedherein to control various switches, and turn all off, or operate all ina same switching state, at about the same time. For example, FIG. 5shows example transformer 400 of FIG. 4 in an example circuitry 500,including a gate drive circuit, switches (e.g., transistors), and anassociated load. However, the concepts described herein are not limitedto use with the structures of transformer 400 or circuitry 500.

In the example of FIG. 5, primary main winding 401 is excited by a mainpulse command associated with different switching state operation oftransistors 501, 502, 503, 504. Primary orthogonal winding 409 isexcited by a shutdown command, e.g., when this shutdown command isreceived, all four transistors 501, 502, 503, 504 are turned off (e.g.,placed in an open circuit state) at about the same time (e.g.,simultaneously). The orthogonal nature of these two sets of windingsallows the main windings to command two of the gate drive signalsapplied to transistors to be in different switching states with theother two, while the orthogonal windings output voltages to all fourgate drive circuits to apply gate drive signals to transistors withidentical phase (and required magnitude to cause all transistors toenter a non-conducting state).

In the example implementation of FIG. 5, transistor 501 corresponds totransistor 110 of FIG. 1, transistor 502 corresponds to transistor 111of FIG. 1, transistor 503 corresponds to transistor 112 of FIG. 1, andtransistor 504 corresponds to transistor 113 of FIG. 1. Accordingly, inan example operation, transistors 501, 504 are driven to conductionwhile transistors 502, 503 are non-conductive; and transistors 502, 503are driven to conduction while transistors 501, 504 are non-conductive.Thus, the operation of transistors 501, 502, 503, 504 when providingsignals to load 508 (in this example, the load is included in an audioamplifier) is, conceptually, the same as the operation of transistors110, 111, 112, 113 of FIG. 1 when providing signals to the load. Forexample, the voltage provided to the load via transistors 501, 504 is indifferent switching states from, and opposite in polarity to, thevoltage applied to the load via transistors 502, 503. In the example ofFIG. 5, the voltage references are +B and −B, which may be anyappropriate different voltages, such as V1 and ground.

In the example implementation of FIG. 5, there is additional controlcircuitry electrically connected between each secondary winding and eachcorresponding transistor. Taking transistor 501 as an example, controlcircuitry 510 includes gate turn-on circuit 511 and gate turn-offcircuit 512. In operation, gate turn-on circuit 511 generates a firstcontrol signal that is based on a signal through secondary main winding404 a. This first control signal is applied to the gate (the controlterminal) of transistor 501 to drive transistor 501 to conduction. Inoperation, gate turn-off circuit 412 generates a second control signalthat is based on a different signal through secondary main winding 404b. This second control signal is applied to the gate (the controlterminal) of transistor 501 to cause transistor 501 not to conduct. Thegate turn-on and gate turn-off circuits of FIG. 5 are operated togenerate appropriate control signals for transistors 501, 502, 503, 504so that transistors 501, 504 are conductive while transistors 502, 503are not conductive, and so that transistors 502, 503 are conductivewhile transistors 501, 504 are not conductive (conceptually, the samemanner of operation as the circuitry described with respect to FIG. 1).

In this example implementation, each gate turn-off circuit (e.g., gateturn-off circuit 512) is also responsive to a signal that is based onthe output of a corresponding secondary orthogonal winding (e.g.,winding 410 a). In response to the signal from the secondary orthogonalwinding, the gate turn-off circuit generates a control signal thatoverrides any control signal from gate turn-on circuit 511. This controlsignal from gate turn-off circuit 512 drives transistor 501 to anon-conductive state (e.g., turns-off transistor 501). In someimplementations, each gate turn-off circuit (four shown in this example)generates a control signal at about the same time, responsive to thesame signal through primary orthogonal winding 409, to operate itscorresponding transistor in a same switching state will all othertransistors controlled by the gate drive circuit (e.g., to turn off-eachtransistor at about the same time). As was the case above, in someimplementations, the transistors all may be turned-off within 200 ns,100 ns, 50 ns, or less following application of a signal to primaryorthogonal winding 409 of the transformer 400. In other implementations,the transistors may be turned-off within a period of time that isgreater than 200 ns.

In some implementations, a gate drive circuit employing primary andsecondary orthogonal windings, such as the gate drive included incircuit 500, also includes compensation circuitry (not shownspecifically in FIG. 5) to reduce noise in the orthogonal signals, whichmay result from lack of symmetry in magnetic structures comprising thetransformers. For example, if there is more than a specified amount ofasymmetry in the structure of a transformer, the magnetic flux path ofthe main windings may not be entirely orthogonal to the magnetic fluxpath of orthogonal windings. In this case, there may be stray signals,such as noise, induced in the main or orthogonal windings atinappropriate times, adversely affecting the operation of the gate drivecircuit. The compensation circuit may be configured to reduce thesestray signals or the effects of the stray signals, thereby compensatingfor the lack of symmetry in magnetic structures comprising thetransformer.

In this regard, FIG. 6 shows an example implementation of a portion 600of circuitry 500 of FIG. 5, which includes a compensation circuit. Inthis example implementation, the compensation circuit includes resistors601, which are selected and configured to set noise thresholds to filterout coupling resulting from stray fields. The stray fields may be causedby transformer windings that are not entirely orthogonal. Other types ofcompensation circuits may be used in addition to, or instead of, theexample depicted in FIG. 6.

In some implementations, the load is, or includes, an audio amplifier orcomponents thereof. However, the gate drive circuit may be used to driveswitches to control any appropriate electrical or electro-mechanicalload or loads.

FIGS. 7A through 7G show structures of an example orthogonal transformerthat may be used in the circuitry described herein. However, thecircuitry is not limited to use with the structures shown in FIGS. 7Athrough 7G, and may be used with any appropriate transformer structure.

Referring to FIG. 7A, a conventional transformer is shown, which isrepresented in FIG. 5 by primary winding 401 (“primary”) and secondarywindings 404 a and 404 b (“secondaries”) (other secondaries are shown inFIG. 5, but only one is depicted in FIG. 7A for simplicity). Inoperation, if current is forced into the dot side of primary 401 (thusis shown the tail of the arrow representing current), current will comeout of the dot sides of secondaries 404 a and 404 b (thus is shown apoint representing the tip of the current arrow). This reflectsconventional transformer operation. Referring to FIG. 7B, the resultingflux path for this operation is shown.

To the structure of FIG. 7A is added a set of a set of orthogonalwindings, such as are represented by orthogonal primary 409 andorthogonal secondary 410 a shown in FIG. 7C. Referring to FIG. 7D,assuming that the flux from primary 401 induced in the center leg of thetransformer splits evenly between the two outer legs of the transformer,when the two windings which comprise 409 are connected as shown, thechange in magnetic field (dB/dt) resulting from voltage applied acrossprimary 401 induces equal and opposite EMFs in the two windings, suchthat the voltage seen across orthogonal primary 409 is zero. Likewise,the voltage seen across orthogonal secondary 410 a is zero.

When current flows through orthogonal primary 409, the resulting flux isshown in FIG. 7E. It can be seen that the fluxes in the center lagcancel, while those in the outer legs reinforce, resulting in a net fluxof FIG. 7F. Because there is no flux in the center leg resulting fromcurrent in orthogonal primary 409 or orthogonal secondary 410A, voltagesapplied to orthogonal primary 409 or orthogonal secondary 410 a will notresult in any voltage induced in windings 401, 404 a or 404 b. This isthe reciprocal to the behavior described previously. Furthermore,windings 409 and 410 a together comprise a transformer, e.g., if currentflows into 409 on the dot side, current will flow out of 410 on the dotside, giving conventional transformer operation with the two windingscoupled through the flux path shown in FIG. 7F. This results in themagnetic system coupling: 401, 404 a and 404 b; and 409 and 410 a. Beingorthogonal, these sets of windings are independent and can transmitinformation and power independent of one another.

Referring to FIG. 7G, it can also be seen that if the transformer is notperfectly symmetrical, the center leg flux does not split exactly intothe two outer legs. This asymmetry results in the two magnetic systemsnot being perfectly orthogonal, resulting in some bleed-through ofsignals between the two. Circuitry to filter or otherwise ignore thiscoupling is described with respect to FIG. 6.

The circuitry described above is not limited to the specificimplementations described herein. For example, the transistors may bereplaced with any appropriate circuitry or other controllable switch orswitching element. There may be different numbers of primary mainwindings, secondary main windings, primary orthogonal windings, andsecondary orthogonal windings than those described herein. There alsomay be different numbers of transistors, and they may be in differentconfigurations, than in the example implementations described herein.Any appropriate control circuitry, and numbers of control circuits, maybe used.

Any “electrical connection” as used herein may imply a direct physicalconnection or a connection that includes intervening components but thatnevertheless allows electrical signals (including wireless signals) toflow between connected components. Any “connection” involving electricalcircuitry mentioned herein, unless stated otherwise, is an electricalconnection and not necessarily a direct physical connection regardlessof whether the word “electrical” is used to modify “connection”.

Elements of different implementations described herein can be combinedto form other implementations not specifically set forth above.

Other implementations not specifically described herein are also withinthe scope of the following claims.

What is claimed is:
 1. Circuitry comprising: a transformer circuitcomprising first windings and second windings, the second windings beingmagnetically orthogonal to the first windings; first transistors toprovide a first voltage to a load, each of the first transistors beingresponsive to a first control signal that is based on a first signalthrough a first winding; second transistors to provide a second voltageto the load, each of the second transistors being responsive to a secondcontrol signal that is based on the first signal through the firstwinding, wherein the first and second control signals cause the firsttransistors to operate in a different switching state than the secondtransistors; and control circuitry responsive to signals receivedthrough the second windings to control the first transistors and thesecond transistors to operate in a same switching state.
 2. Thecircuitry of claim 1, further comprising: a control circuit between eachfirst winding and each first and second transistor, each control circuitbeing configured to generate either the first control signal or thesecond control signal.
 3. The circuitry of claim 1, wherein the controlcircuitry comprises circuits, each of which is between a secondarywinding and a corresponding transistor.
 4. The circuitry of claim 1,wherein the first transistors comprise a first transistor connectedbetween the first voltage and the load and a second transistor connectedbetween the load and a reference voltage; wherein the second transistorscomprise a third transistor connected between the first voltage and theload and a fourth transistor connected between the load voltage and thereference voltage.
 5. The circuitry of claim 4, wherein the firsttransistor and the fourth transistor are operational in a same switchingstate to apply the first voltage to the load, and the second transistorand the third transistor are operational in a same switching state toapply the second voltage to the load, the second voltage being equal inmagnitude and opposite in polarity to the first voltage.
 6. Thecircuitry of claim 5, wherein the first transistor and the fourthtransistor are conductive while the second transistor and the thirdtransistor are not conductive, and the first transistor and the fourthtransistor are not conductive while the second transistor and the thirdtransistor are conductive.
 7. The circuitry of claim 6, wherein thefirst transistor, the second transistor, the third transistor, and thefourth transistor are field effect transistors (FETs), each of the FETscomprising a control terminal for receiving either the first controlsignal or the second control signal.
 8. The circuitry of claim 1,wherein the control circuitry is configured to generate a third controlsignal that is applicable to gates of the first and second transistors.9. The circuitry of claim 1, wherein control of the first transistorsand the second transistors to be in a same switching state occurs, atmost, within 200 nanoseconds of a command instructing that thetransistors operate in a same switching state.
 10. The circuitry ofclaim 1, wherein control of the first transistors and the secondtransistors to be in a same switching state occurs, at most, within 100nanoseconds of a command instructing that the transistors operate in asame switching state.
 11. The circuitry of claim 1, further comprising:compensation circuitry to reduce noise resulting from lack of symmetryin magnetic structures comprising the transformer circuit.
 12. Thecircuitry of claim 1, wherein the first windings and the second windingsare secondary windings of a transformer circuit having at least oneprimary winding.
 13. The circuitry of claim 1, wherein the transformercircuit comprises a main primary winding and an orthogonal primarywinding, the main primary winding for inducing signals in the firstwindings and the orthogonal primary winding for inducing signals in thesecond windings.
 14. The circuitry of claim 1, wherein the load is partof an audio amplifier.
 15. The circuitry of claim 1, wherein the controlcircuitry is configured to override the first control signal and thesecond control signal to cause the first transistors and the secondtransistors to be in a same switching state.
 16. The circuitry of claim1, wherein the control circuitry is configured to override the firstcontrol signal and the second control signal to cause the firsttransistors and the second transistors to be non-conductive. 17.Circuitry comprising: a transformer circuit comprising first windingsand second windings, the second windings being magnetically orthogonalto the first windings; and control circuitry (i) responsive to signalsin the first windings, to cause application of a first voltage and asecond voltage to a load, the application of the first voltage and thesecond voltage being applied at different times and in oppositepolarity, and (ii) responsive to signals in the second windings toprevent application of either the first voltage or the second voltage tothe load.
 18. The circuitry of claim 17, further comprising: switchesthat are controllable based on the signals in the first windings toenable application of either the first voltage or the second voltage tothe load, the switches also being controllable to open based on thesignals in the second windings, thereby preventing application of eitherthe first voltage or the second voltage to the load.
 19. The circuitryof claim 17, wherein the first and second windings comprise secondarywindings of the transformer circuit, and wherein the transformer circuitcomprises one or more primary windings to receive control signals forcontrolling the circuitry.
 20. Circuitry comprising: a transformercircuit comprising first windings and second windings, the secondwindings being magnetically orthogonal to the first windings; meansresponsive to first control signals that are based on first signalsthrough first windings to provide a first voltage to a load; meansresponsive to second control signals that are based on the first signalsthrough the first windings to provide a second voltage to the load,wherein the first control signals and the second controls signal causeoutput of the first voltage to be opposite in polarity to the secondvoltage; and means responsive to third signals received via secondwindings to override the first signals to cease output of the firstvoltage or the second voltage from the circuitry.